What happens in a circuit on the secondary side of a current transformer (CT) with an open connection on a fully loaded line?

In a current transformer (CT), when the secondary side is open-circuited while the primary side is carrying a full load current, it can lead to a dangerous situation characterized by overvoltage conditions on the CT. This happens because the CT is designed to convert high currents from the primary circuit into lower proportional currents for measurement and protection purposes. When the secondary circuit is open, there is no path for the current to flow.

As a result, the coil of the CT can generate a very high voltage due to the magnetic field created by the primary current. The energy has no load to dissipate, leading to an increase in voltage that can exceed the design limits of the transformer, potentially damaging the CT or connected equipment. Therefore, recognizing the risk of overvoltage on the secondary side of a CT is crucial for ensuring the safety and reliability of electrical systems.

This situation emphasizes the importance of proper connections and protective measures in a system using current transformers to prevent hazardous conditions caused by open circuits.